HR: 0800h
AN: T21B-0599    [Abstracts]
TI: French Polynesia Hotspot Swells Explained By Dynamic Topography
AU: * Adam, C
EM: adam@jamstec.go.jp
AF: IFREE JAMSTEC, 2-15 Natshushima-cho, Yokosuka, 237 0061, Japan
AU: Yoshida, M
EM: myoshida@jamstec.go.jp
AF: IFREE JAMSTEC, 2-15 Natshushima-cho, Yokosuka, 237 0061, Japan
AU: Isse, T
EM: isse@jamstec.go.jp
AF: IFREE JAMSTEC, 2-15 Natshushima-cho, Yokosuka, 237 0061, Japan
AU: Suetsugu, D
EM: dai@jamstec.go.jp
AF: IFREE JAMSTEC, 2-15 Natshushima-cho, Yokosuka, 237 0061, Japan
AU: Shiobara, H
EM: shio@eri.u-tokyo.ac.jp
AF: ERI, Univ. of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113 0032, Japan
AU: Sugioka, H
EM: hikari@jamstec.go.jp
AF: IFREE JAMSTEC, 2-15 Natshushima-cho, Yokosuka, 237 0061, Japan
AU: Kanazawa, T
EM: kanazawa@eri.u-tokyo.ac.jp
AF: ERI, Univ. of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113 0032, Japan
AU: Fukao, Y
EM: fukao@jamstec.go.jp
AF: IFREE JAMSTEC, 2-15 Natshushima-cho, Yokosuka, 237 0061, Japan
AU: Barruol, G
EM: Guilhem.Barruol@univ-montp2.fr
AF: Montpellier II Univ., pl Eugène Bataillon, Montpellier, 34090, France
AB: Situated on the South Pacific Superswell, French Polynesia is a region characterized by numerous geophysical anomalies among which a high volcanism concentration. Seven hotspots are required to explain the observed chains, volcanism ages and geochemical trends. Many open questions still remain on the origin of these hotspot chains: are they created by passive uplift of magma due to discontinuities in the structure of the lithosphere or by the ascent of mantle plumes? In this case, at which depth do these plumes initiate in the mantle? Many geophysical observations (bathymetry, gravity, magnetism, volcanism ages..) are used to understand the unique phenomenon occurring on this region. The most useful information may come from tomography models since they provide a 3D view of the mantle. Until recently, the tomography models over the region were quite inaccurate because of the sparse location of the seismic stations. The deployment of two new seismic stations networks (BBOBS and temporary island stations) has lately remedied this failing. The resulting tomography model obtained through the inversion of Rayleigh waves provides the most accurate view of the shallowest part of the mantle (depths ≤ 240 km) beneath French Polynesia. Indeed, for the first time the accuracy of a tomography model is good enough to provide information about plume phenomenology in this complex region. In order to quantify the plumes effect on the seafloor, we compute the dynamic topography through an instantaneous flow model. The general trend of the observed depths anomalies (highs and lows) is well recovered. For example the amplitude, location and extension of the swells associated with the Society, Macdonald and Rarotonga are accurately described by the dynamic model. We also find that dynamic uplift is associated with the Tuamotu archipelago which means that a part of the observed swell is due to the present day action of plumes. Since no volcanism ages are available over this chain, this new information may be quite important in understanding the archipelago origin. Another interesting result is that Arago, which is supposed to be an active hotspot along the Cook-Austral chain is situated on a bathymetric low which is well recovered by the dynamic model. Since this region is associated with downwelling flows, this makes us question its hotspot origin.
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 4255 Numerical modeling (0545, 0560)
DE: 7270 Tomography (6982, 8180)
DE: 9355 Pacific Ocean
SC: Tectonophysics [T]
MN: 2007 Fall Meeting